Learn English as a second language
Young multiple-language learners develop the same Broca's area and left inferior frontal lobe of the brain for all their languages. Those learning their second language after the critical period that ends between 5 and puberty develop their second language region in a different location of the Broca's area. It is much easier to learn multiple languages before the critical period.
Exposing multiple languages to an infant may boost his language learning capability later.
Most people learn non-native languages primarily after the critical period. They need to develop new areas in the brain for non-native languages. Unfortunately, they often learn non-native languages by translating from their native languages. In other words, they keep jumping back to their native language region. Translation or language switching requires another region to be activated. Bilingual dictionaries have their use, but they do more harm than good for learning non-native language because they enforce the link between two languages.
The only way to be fluent in a language is by restricting the entire process of language use within one language region. In other words, one needs to think only in the language in use and avoid any translation.
Many adults eagerly jump to a level equal to that of their native language when learning a non-native language, and rely on the translation from their native language to comprehend the non-native language. It appears to be a shortcut, but actually is a flawed approach that not only prohibits the true comprehension of the non-native language but also wastes time. It is faster to start from simple picture books to link the words of a non-native language with images as the case for the native language and advance as fast as possible to higher levels.
It is common to see people who have studied a non-native language for decades, but their level is no better than that of 2nd or 3rd-grade kids learning it as their native language. If an adult starts from kindergarten picture books, he can easily move through 1st grade, 2nd grade, and 3rd grade within a year in his spare time and reach a level sufficient to use the language for daily life (e.g. listening to or reading news) within 2 years. Once he reaches this level, he can start using the language for his interests or work and keep learning while using it. All this can be done in one's spare time.
Learning a language is similar to learning most other skills. Most of the learning eventually will come from practicing or using it in daily life or work. Once one reaches the point of being able to use a non-native language for practical use, the progress will be automatic without dedicating time to study the language.
The following resources may be helpful in getting to that point:
United has excellent picture books to learn basic words used daily for beginners.
British Council has excellent materials for English learners of different levels.
VOA Learning English has excellent lessons for different levels.
BBC Learning English is good for the intermediate to advanced levels.